zdtm: close __file_report before executing tests

------------------------ grep Error ------------------------
(00.011453) Error (files-reg.c:1136): Can't lookup mount=85 for fd=3 path=/var/lib/jenkins/workspace/CRIU-inhfd/test/report/criu-testreport.tap
(00.011478) Error (cr-dump.c:1304): Dump files (pid: 4) failed with -1
(00.011903) Error (cr-dump.c:1606): Dumping FAILED.
------------------------ ERROR OVER ------------------------

Cc: Sergey Bronnikov <sergeyb@openvz.org>
Fixes: c4e13bc92816 ("zdtm.py: add support of test reports in TAP format")
Signed-off-by: Andrew Vagin <avagin@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

test/zdtm.py

@@ -1071,7 +1071,7 @@ class launcher:
 
 		sub = subprocess.Popen(["./zdtm_ct", "zdtm.py"], \
 				env = dict(os.environ, CR_CT_TEST_INFO = arg ), \
-				stdout = log, stderr = subprocess.STDOUT)
+				stdout = log, stderr = subprocess.STDOUT, close_fds = True)
 		self.__subs[sub.pid] = { 'sub': sub, 'log': logf, 'name': name }
 
 		if test_flag(desc, 'excl'):